Influence of covalent character on high Li ion conductivity in a perovskite-type Li ion conductor: Prediction from a molecular dynamics simulation of La_0.6Li_0.2TiO₃

We executed a molecular dynamics simulation for the perovskite-type high Li ion conductor, La_0.6Li_0.2TiO₃, using two different potential models, the fully ionic model (FIM) and the partially ionic model (PIM). Good reproducibility of the physical properties was obtained for the simulation using the PIM. While displacement of the Li ion from the A-site was indicated in both models, Li ion diffusion was observed only for the PIM below 600 K. These results suggest that the introduction of a small mobile ion into the A-site does not always induce high ion conduction and that the covalent character of the Ti-O bond is indispensable to the high Li ion conduction. The ionic conductivity, however, could not reproduce quantitatively in this simulation due to the random distribution of A-site ions in the simulation cell.